This invention relates to instrumentation for implanting a prosthetic hinged knee. More particularly, it relates to instrumentation for locating the internal/external rotation of the tibial component of the hinged knee on a resected tibia.
According to one preferred aspect of the present invention there is provided a total knee replacement prosthesis (TKR) which comprises a femoral component which is pivotably connected to a tibial component at a hinge for pivoting movement about a medial-lateral axis. One portion of the hinge is preferably formed on the femoral component. The preferred tibial hinge component is rotably received within a bearing component adapted to be mounted on a tibial baseplate having a stem implanted in the tibial intramedullary canal, so that the tibial hinge component is rotatable within the bearing component to provide a degree of internal/external rotational freedom of movement for the prosthesis. The preferred femoral component includes a stem portion for implantation within the canal of the femur.
In general, the tibial and femoral components are constructed from a metal which is biomedically inert, e.g. a stainless steel, a cobalt-chromium-molybdenum alloy such as Vitallium(copyright) alloy or a titanium alloy. The bearing components should preferably exhibit low friction with respect to the component which rotates within them and typically materials which meet this requirement are polyolefines. Particularly, preferred materials for this purposes are ultra-high molecular weight polyethylenes. Preferably, the rotational movement takes place by rotation of a tibial stem within a tubular or hollow bearing component which is fixed relatively to the tibia. Thus, for example, the tibial hinge component may comprise a distally facing surface with a stem portion extending distally and a hinge portion for connection to the femoral component at its proximal end. At the distal end the stem is received in the bearing component with the distally facing surface rotating on the proximal bearing surface. The tibial baseplate component may have an internal bore dimensioned to receive the tibial hinge component stem and an external surface suitably sized to fit the tibial bone canal.
In a preferred embodiment, the tibial and femoral components are pivotably connected by a hinge. Such a hinge has a pin or axle which passes through aligned bores in the two components. In the preferred embodiment, each condyle of the femoral component includes a hinge part and the tibial component includes a centrally located hinge part extending within the intra-condylar notch of the femoral component. Bushings may be used in the bores of the hinge parts for improved wear and reduced friction. These bushings may be made of plastic such as ultra-high molecular weight polyethylene. Alternatively, the femoral component may include a body portion which has a bore to receive the hinge pin and the tibial component may include a pair of ears or lugs which extend on each side of the body portion of the femoral component. The hinge pin or axle is preferably removably fixed by suitable locking means, such as circlips in apertures in the hinge parts. Thus, the femoral and tibial components can be installed in their relative intramedullary canals and the joint made by introducing the hinge pin and the locking means.
Such a prosthetic hinge knee joint is taught in U.S. Pat. No. 4,301,553, the teachings of which are incorporated herein by reference. With this hinged knee design as well as many later designs, there has been a need to facilitate the rotational alignment of the tibial and femoral components with respect to the patients anatomy so that once the hinge pin is inserted between the femoral component and the tibial components and the components fixed to the distal femur and proximal tibia, the soft tissue balance produces a natural gate after implantation.
Often a modular rotating hinged knee system is designed for knees with severe joint destruction and/or ligament instability where a condylar style non-hinged implant is not appropriate. While the hinge mechanism has been designed for those knees in which the soft tissue envelope is compromised, where possible, the collateral ligaments should be preserved to enhance the longevity of the device. In order to accomplish this, the proper tension of the knee must be maintained by the soft tissue, thus requiring a trial reduction to ensure correction of the alignment instability along with an estimation of the range of motion of the prosthesis after implantation.
Currently, there is a need for a method of determining the optimal rotational orientation of the tibial baseplate of a hinged knee prosthesis prior to its permanent implantation on the proximal tibia. There has particularly been a need for instrumentation which would allow the surgeon to set the internal/external rotation of the foot and optimize the patellar tracking along the femoral component before the tibia is resurfaced.
U.S. Pat. Nos. 6,228,091 and 6,258,095 disclose methods and instruments for resecting the distal femur and proximal tibia in a manner similar described herein. The teachings of these patents are incorporated herein by reference. The tibial rotation guide of the present invention is intended to be used in a procedure similar to that described in U.S. Pat. No. 6,228,091 but tailored for use with a hinged knee prosthesis.
It is an object of the invention to provide an instrument which allows the determination of the correct internal/external rotation of the tibial component after the location and implantation of a femoral component or a femoral trial has been accomplished.
It is an additional object of the invention to provide an instrument which is capable of locating the proper internal/external rotation of both the hinged tibial component and the hinged femoral component after the femoral component has been located on a prepared distal femur but prior to the location of the tibial component on a resected proximal tibia.
These and other objects of the invention are accomplished by a tibial rotation guide having two modular parts, the first part being a trial tibial template and the second part being a hinge part. The hinge part being removably coupled to the first part, and includes a hinge portion for coupling the trial tibial component to a hinged portion of the hinged femoral component. The two part tibial rotation guide is assembled and coupled to the hinged connection on the located femoral component allowing the surgeon to then place the previously resected proximal tibia flush against the underside of the tibial template. Joint space, range of motion, leg length and tissue balance can then be evaluated.
The tibial rotation guide includes a plurality of tibial templates and hinge parts which, when assembled with its mating components on the femur, mimic the various tibial baseplate insert thicknesses. Therefore, if the joint space between the femoral component and the tibial component of the prosthesis is not appropriate, the surgeon may select a different tibial rotation guide which represents the next available insert thickness and sizes. This step may be repeated until the appropriate joint space is achieved. In addition, various sizes of trial tibial templates are provided to correspond to various sizes of resected proximal tibias. A tibial alignment handle may also be assembled to the tibial template to help to verify alignment of the tibial axis in the medial-lateral and anterior-posterior planes. An alignment pin may extend from the alignment handle in a proximal-distal direction for alignment purposes. In addition, the patella may be placed back over the femoral component and while maintaining the proximal tibia flush against the underside of the template the tibia may be internally and externally rotated until optimal patella tracking is achieved in conjunction with the femoral component. The template is then fixed to the tibia and the joint can be flexed through its range of motion to further evaluate patella tracking. Finally, the hinged part of the tibial rotation guide can be disassembled from both the femoral component and the tibial template and tibial baseplate preparation can begin.
If it is desired to orient the femoral component rather than initially locating the femoral component on a fully prepared distal femur, the trial femoral component is inserted into the prepared femoral canal in a manner described hereinbelow which allows rotation with respect to the unprepared distal femur. The tibial rotation guide is then assembled as above and coupled to the hinge on the trial femoral component and the internal/external rotation of the femur and tibial component are set in a manner which optimizes patella tracking and range of motion.